This invention is concerned with the purification of molybdenum. Examples thereof are shown in the following U.S. Pat. Nos. 4,933,152; 4,814,148; 4,735,791; 4,702,895; 4,643,884; 4,604,267; 4,604,266; 4,601,890; 4,596,701; 4,555,386; 4,525,331; 4,207,296.